Cam with separated peripheral surfaces

ABSTRACT

This invention belongs to projectile throwing instruments that use the energy of the strained hard body and can be used for the design and construction of a missile throwing weapon—namely for a bow and crossbow.

This invention belongs to projectile throwing instruments that use the energy of the strained hard body and can be used for the design and construction of a missile throwing weapon—namely for a bow and crossbow.

Since the middle of the 20^(th) century, these cams have been widely used for the designing of bows and crossbows. According to the common technique, the cams have at least two peripheral surfaces on which a working bowstring and cable strings are placed. The cams are mainly placed on the free ends of the limbs. The main characteristic feature and advantage of cam usage in the projectile throwing instrument design is the release of the pulling force in the tension endpoint and the increase of the thrown projectile's speed at the moment of its shooting. In addition, cam throwing devices are the fastest and are rather compact. All of the technical solutions that aimed to perfect the design of the projectile throwing instrument according to the previous technical level are mainly directed towards changing the geometrical shape of the cam. However, with all the diversity of cam shapes and designs, all of them have two common characteristic features. The first one is the cam peripheral surfaces' location in the middle part of the holding axle by means of which the cam is fixed onto a limb. Secondly, the peripheral surfaces are situated at a short distance from each other. In such a location of the peripheral surfaces, the cable strings are located near the working bowstring and hinder the path of the thrown missile. That is why during the design of projectile throwing instruments there appears the necessity to forcedly turn the cable strings away from the working string. For this, various constructions of cable string retractor assemblies are used. The main drawback in the well-known cam constructions is that they cause additional friction on the joints and spiral torsional strains that are passed by the cable strings to the limbs.

There is a well-known design (U.S. Pat. No. 6,659,096B1), which contains a cam fixed onto the flexible element's free end, which is able to spin and has peripheral surfaces that give way to the working string and cable strings. These surfaces are situated in the middle part of the cam's axle that is fixed to the limb at a short distance from one another.

The main drawback of the bow mentioned above is the necessity to turn the cable strings away from the working string.

There is a crossbow design (U.S. Pat. No. 6,460,528 B1) that contains the cam fixed on the flexible element's free end, which is able to spin and has peripheral surfaces that give way to the working string and cable strings. These surfaces are situated in the middle part of the cam's axle that is fixed to the limb at a short distance from one another.

The main drawback of the crossbow mentioned above is the necessity to turn the cable strings away from the working string.

The technical problem, which is to be solved by means of the given invention implies the creation of an improved cam design that will allow for the manufacturing of cam throwers without turning away the joints of the cable strings, which in its turn will increase the efficiency of the work of the limbs.

The technical result provided by the usage of the present invention consists in the increase of the maximum starting speed of the thrown missile, improved shooting accuracy and density, as well as the decrease of its noise and vibration.

To achieve the mentioned technical result it is recommended to use the divided cam of the bow or crossbow's string tension that are placed on the flexible element's free end, which is able to spin and has peripheral surfaces that give way to the working string and at least one cable string, in which this string's peripheral surface is located at the nearest peripheral surface of the cable string at a distance at which the cable string does not in any way obstruct the path of the thrown missile.

The cam represents the spinning part of a wheel shape or of a complex non-round shape including the shifted spinning axis.

The system consisting of at least one designed cam and containing limbs with free ends is to be placed on the projectile throwing instrument. On the free ends the cams able to spin, and they have peripheral surfaces that give way to the string and cable strings. With this, the string's peripheral surface stands from the cable strings' peripheral surfaces at a distance that is enough to expel the joint of the cable strings' peripheral surfaces and turn-away out of the projectile throwing instrument's design.

In most cases, the divided cam represents the spinning part of the round, elliptic, or any other shape known in the given branch of engineering. The peripheral surface, which is shaped like a string channel, is situated in the upper part of the cam. In the lower part of the cam, at least one peripheral surface for cable strings is located. The middle part of the divided cam serves to separate the string's peripheral surface and cable strings' peripheral surfaces within a distance at which the cable strings do not prevent shooting. The upper and lower parts of the divided cam are firmly interconnected and turn around the spinning axis synchronously. The constructive use of the divided cam and used materials can be various and can be used in the given branch of engineering. To decrease the size, the limbs can be placed in the middle part of the divided cam between the string's peripheral surface and the cable strings' peripheral surface. The divided cam's spinning axis can go through the cam's center or be shifted relative to the cam's center. Cable strings can be placed on the peripheral surfaces in the cam's lower part in parallel or intercross.

The divided cams can be placed on the crossbow, on the bow, or on any other suitable projectile throwing instrument.

Furthermore, the present invention will be described in detail using diagrams.

FIG. 1 shows the system of cams with the joint of cable strings' turn-away according to the known engineering level.

FIG. 2 shows the system of divided cams with crossed cable strings according to the present invention.

FIG. 3 shows the system of divided cams with parallel cable strings according to the present invention.

The following legend is used in the diagrams: limbs 1, cam's holding axis 2, cam accordingly to the known engineering level 3, string's peripheral surface 4, peripheral surface for one cable string 5, peripheral surface for another cable string 6, thrown missile 7, joint of cable strings' turn-away 8, the string's path of motion 9, motion path of one cable string 10, motion path of another cable string 11, middle part of divided cam 12, upper part of divided cam 13, and the lower part of divided cam 14.

Preparation and shooting of the bow or crossbow using the designed cam construction does not differ from the preparation and shooting of a bow or crossbow using the cam-prototype.

The use of the mentioned technical solution allows for an increase of the maximum starting speed of the thrown projectile by approximately 15%, accuracy and the density of shooting by approximately 10%, and at the same time a decrease in the noise and vibration of the shooting. 

1. A cam with separated peripheral surfaces for the projectile throwing instrument is installed on the free end of the thrower's limb, which is able to spin and has peripheral surfaces that give way to the string and cable strings. With this, the string's peripheral surface stands from the cable strings' peripheral surfaces at a distance far enough to allow for the string and at least one cable string, in which the distance between the string's peripheral surface and the nearest peripheral surface is enough for the cable string not to hinder the path of the thrown projectile. Moreover, the cable strings are completely intercrossed.
 2. The cam of claim 1 wherein the cable strings are not intercrossed.
 3. The cam of claim 1 wherein the symmetry axis coincides with the spinning axis.
 4. The cam of claim 1 wherein the symmetry axis stands off from the spinning axis.
 5. The cam of claim 1 wherein the cam is of a round shape.
 6. The cam of claim 1 wherein the cam is of a non-round shape. 